1 Field of the Invention
The invention relates to a process for preparing organosilicon compounds containing amino groups, these compounds containing no fraction, or a very small fraction, of silanol groups.
2 Description of the Related Art
Processes for preparing organosilicon compounds containing amino groups are already known. U.S. Pat. No. 5,461,134 describes an equilibration process for preparing aminoalkyl-terminal siloxanes having chain lengths of more than 50 silicon atoms. A catalyst used is anhydrous tetramethylammonium hydroxide-aminopropyldimethyl-silanolate. Furthermore, EP-A 739 372 describes an equilibration process for preparing aminoalkyl-terminal siloxanes having chain lengths of more than 27 silicon atoms. Catalysts used are Rb or Cs hydroxides/silanolates, which after the end of the reaction must be neutralized with acids, and the salts must be removed by filtration.
The processes known to date oftentimes have the disadvantage that, owing to the incorporation of the traces of moisture that are present, compounds with a high silanol fraction are obtained. Reducing the unwanted silanol fraction usually entails a significantly increased process cost and inconvenience.
For numerous applications of the amino-functional siloxanes, such as copolymerization with diisocyanates, acid esters, and acid chlorides, a low silanol fraction is massively important. Si—OH groups have proven particularly disadvantageous in the context of copolymerizations to form polyureas, since the Si—OH groups act as chain terminators in the subsequent poly-addition reaction with diisocyanates. The significance of this problem grows in line with increasing chain length of the polysiloxane, because the number of active end groups falls as the siloxane chain length grows.